1. Field of the Invention
The invention pertains to the field of protein chemistry and, more particularly, to short-chain peptides that serve to modulate interprotein interactions. More specifically, these short chain peptides have functional residue sequences that essentially replicate fragments of functional domain sequences in corresponding parent protein molecules, but without replicating the entire parent protein. A first such peptide may be mixed with a second peptide to enhance the functionality of the first peptide by inducing a conformational change in a target protein that is reactive with the first peptide. Similarly, the second peptide may induce a conformational change in the first peptide. Particularly preferred short-chain peptides are taken from parent protein molecule sequences selected from the family of integrins, proteins that react with integrins, and the superfamily of immunoglobulins. The peptides are utilized according to methods including the steps of providing the peptides and applying them to a population of cells.
2. Description of the Prior Art
Certain immune system functions rely upon a critical interprotein binding interaction as a necessary element of immune response. One such binding interaction pertains to a heterophilic interaction between the glycoproteins including Intercellular Adhesion Molecule ("ICAM-1") and Leucocyte Function Associated antigen-1 ("LFA-1"). Examples of published sequences for LFA-1 and ICAM-1 are submitted as Sequence ID No.'s 1, 2, and 3.
It is possible to derive immunological benefits by disrupting the intercellular ICAM/LFA binding interaction through the application of specific monoclonal antibodies ("mAbs"), i.e., anti-ICAM-1 or anti-LFA-1. As reported in Isobe et al., Specific Acceptance of Cardiac Allograft After Treatment With Antibodies to ICAM-1 and LFA-1, 255 SCIENCE 1125-1127 (Feb. 1992), an induced immune tolerance enables the indefinite survival of cardiac allografts between fully incompatible mouse strains subsequent to a six day treatment including the simultaneous application of anti-ICAM-1 and anti-LFA-1 mAbs. Unfortunately, a major problem with the use of mAbs for the purpose of inducing immune-tolerance in a mammal is that these large (e.g., 80-150 kDa) molecules typically also induce an effectiveness-limiting immune response to the mAbs.
LFA-1 has special significance in that it belongs to a family or class of proteins that are known as integrins, and is associated with leukocytes such as T and B cells. The integrin family includes similar glycoproteins that combine two separate protein units as a functional member, i.e., a functional heterodimer formed of a .beta. unit and an .alpha. unit. These respective units each comprise separate proteins that are anchored within interactive proximity to one another, and can extend outwardly from a cytoplasmic domain, across a transmembrane domain, and beyond the cell membrane. In LFA-1, binding avidity for ICAM-1 involves Mg.sup.2+ and Ca.sup.2+ ions that, in part, govern the interaction between the .beta. and .alpha. units.
The integrin family may be subdivided into two groups wherein common group members share common .beta. units. A first group of proteins share the common .beta.1 (CD29) unit, and typically function by binding to extracellular matrix proteins. This first group includes the VLA-1 (CD49a/CD29), VLA-2 (CD49b/CD29), VLA-3 (CD49c/CD29), VLA-4 (CD49d/CD29), VLA-5 (CD49e/CD29) and VLA-6 (CD49f/CD29) proteins. A second group shares the .beta.2 unit (CD18), and typically functions in cell to cell interactions. This second group includes LFA-1 (CD18/CD11a), MAC-1 (CD18/CD11b), and p150,95 (CD18/CD11c). The LFA-1.alpha. unit (CD11a protein, i.e., Sequence ID No. 2) is the specific heterodimer counterpart to the .beta.2 unit in LFA-1.
Li et al., A Leukocyte Integrin Binding Peptide from Intercellular Adhesion Molecule-2 Stimulates T Cell Adhesion and Natural Killer Cell Activity, 268 J. Biol. Chem. 21474-21477 (Jul. 20, 1993), report that .beta.2 integrins, and particularly LFA-1, have a cytoplasmic domain which serves to alter protein configuration via a cellular phosphorylation pathway communicating the integrin and respective cell receptor areas. That is to say, phosphorylation may be activated at a remote receptor site with the result of indirectly inducing conformational changes in the integrin via cytoplasmic phosphorylation.
On the other hand, ICAM-1 proteins are not known to incur phosphorylation induced conformational changes. ICAM-1 is found primarily upon monocytes and endothelial cells, and is widely inducible, or upregulated, on many cells including B and T lymphocytes, thymocytes, dendritic cells, endothelial cells, fibroblasts, keratinocytes, chondrocytes, and epithelial cells. This protein has a co-stimulatory effect upon cytotoxic T-cell interaction, and is utilized in a number of intercellular binding interactions.
Recent developments in the field of protein chemistry confirm that short-chain peptides, which have amino acid residue sequences representing mere fragments of a corresponding parent protein molecule, may exhibit significant levels of biofunctionality. Short-chain peptides that derive from the ICAM-1 protein are known to have utility in blocking binding interactions between cells and viruses. Even so, only a very limited number of specific ICAM-1 based peptides have been shown to be useful.
European Patent Publication No. EP 391,088 A2 indicates that functional derivatives of the intercellular adhesion molecule ("ICAM-1") may be used in anti-viral therapy. These functional derivatives may include functional domains and fragments of the ICAM-1 molecule. The method of using these fragments includes administering them in a manner that prevents viral infection of potential viral host cells by impairing a binding interaction between the cells and rhinoviruses that may contact the cells. The binding interaction to be impaired includes one between an ICAM-1 cellular receptor and a corresponding viral adhesion site. The ICAM-1 fragments impair the cell-to-virus binding interaction by competing with normal cellular ICAM-1 molecules for adhesion to the corresponding viral binding site.
Another publication, PCT/AU91/00205, describes the use of short-chain ICAM-1 based peptides for inhibiting intercellular adhesion in mammals.